The disclosure herein relates to thrust bearing assemblies that typically comprise a retainer ring encompassing a plurality of thrust bearing pads arranged in circumferential spaced relationship around a shaft axis. A shaft that is to be axially supported for rotation usually has a radially extending collar providing a bearing surface that interfaces with the circular array of thrust pads which are bathed in a fluid, such as oil, which lubricates and cools the bearings. The thrust pads are customarily supported on a circular array of overlapping pivotal upper and lower leveling links that transmit forces between each other to equalize the load on the thrust pads. The pads are free to tilt to a limited extent so as to develop a wedge-shaped film of lubricant that supports the load. To equalize the load among the pads, the leveling links lower the overloaded thrust pad and raise the underloaded thrust pads. Since the leveling links are in contact, any unbalanced forces are transmitted through the leveling links until equilibrium is reached. The retainer or base through which the load on the shaft is transmitted to ground or the machine frame is in the form of an annular channel having a closed bottom and an open top and in which the leveling links and tilting bearing pads reside.
Whether the shaft is turning about a horizontal axis or a vertical axis, a thrust bearing assembly is encased in a housing through which the oil is forced at relatively low pressure for cooling and lubricating the bearings. Flat bronze floating ring seals are installed on the shaft on each side of the bearing assembly. These ring seals act as a barrier against flow or leakage of cooling oil along the longitudinal surface of the shaft. There is a small clearance between the shaft and the inside of the ring so the shaft can rotate without dragging the seal around with it. A design that permits getting rid of these floating ring seals would be desirable because, they not only add to manufacturing costs, but they do produce some non-useful energy dissipation because of the shear forces that are developed in the lubricant between rotating and stationary parts.
Conventional hydrodynamic thrust bearings used in high speed machinery require circulating, a large quantity of lubricating oil through the bearing housing at low pressure. The practical effect is that high capacity circulating pumps are necessary which increases system costs. In addition, if lubricating oil flow rate can be reduced, the size of other elements in the cooling system can be reduced such as the oil sump, heat exchangers, valves, filters and other fittings.
The thrust pads whose leading edges must tilt away from the load transmitting collar on the shaft in order to form a wedge of lubricating oil between the collar and pads are usually cut from a solid ring of bearing material. More specifically, the ring comprises a steel annulus on one surface of which there is a coating of babbitt or other low friction material. The annulus or ring is then milled or sawed along radial lines to divide it into a number of sectors or generally pie-shaped segments. In conventional tilting pad bearing assemblies which use high flow lubricating and cooling systems, a substantial amount of space is allowed between the leading edge of one pad and the trailing edge of the next preceding pad all the way around the circular array of pads in the retainer. The leading and trailing edges of the pads are machined to fairly high accuracy after they are sawed since they must fit in the annular channel of the retainer with enough clearance on their radially inward and outward ends to permit a slight amount of tilting during operation without jamming up against the walls of the retainer. No provision is made in conventional bearings for radial inward or outward adjustment of the bearing pads. The gaps between pads defined by the trailing edge of one pad and the leading edge of the adjacent pad must be rather large because these gaps are major passageways for the lubricating and cooling fluid flow. Under these conditions, there is no way to control the amount of leakage flow at the gap between pads for bearings with low surface frictional drag properties. This can be disadvantageous because it prevents conventional bearings from performing properly at low oil flow.
Expired U.S. Pat. No. 2,507,021 to Lakey appears on first impression to have a feature which might possibly solve some of the problems in conventional bearings which are discussed above The feature of interest is a radially extending groove or channel which is formed in the load bearing face of the pads, particularly inwardly from and in parallelism with the leading edge of the pads. The groove, of course, is open at its top and has closed ends. A tube feeds oil into the bottom of the groove so it fills the groove with oil. The reason for supplying oil to the pads in the region of the groove is to compensate for the amount of oil that is centrifuged radially outwardly of the pad surfaces by rotation of the interfacing load transmitting surface on the collar. The oil is fed through a duct under each pad which duct is connected to the input port or bottom hole in the groove by means of a connecting tube which has spherical outside ends so that the pads can tilt without being blocked by the tube. Because the radially extending groove is set inwardly from a radially extending leading edge of the pad there is no provision for controlling the amount of fluid that flows into the gap between pads as is the case with the invention described herein.